Bach 11 vs Kelly MC
The Kelly MC has a wider cup diameter, the Kelly MC features a deeper cup, the Bach 11 has a larger throat opening.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 11
• French Horn
Cup diameter16.55 mm / 0.6516 in
Best suited for
All-round versatile — balanced cup for general playing
High-volume projection — open throat for power
vs
Mouthpiece B
Kelly MC
• French Horn
GeneralCup diameter16.76 mm / 0.6598 in
Best suited for
High-volume projection — open throat for power
All-purpose French horn
Cup Diameter
The Kelly MC has a cup diameter of 16.76 mm / 0.6598 in compared to 16.55 mm / 0.6516 in on the Bach 11 — a difference of 0.21 mm / 0.0083 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.